摘要
永泰云山早白垩世石帽山群第Ⅰ、Ⅱ旋回岩石组合由沉积岩、基性熔岩、酸性火山岩构成，缺乏中性成分的岩石单元，为典型的双峰式岩石组合。其玄武岩富碱（尤其富钾）、富铝、富铁，贫镁，富轻稀土元素和大离子亲石元素，贫高场强元素及亲铁元素，并具偏高的ＩＳｒ值和显著偏低的εＮｄ（Ｔ）值［ＩＳｒ＝０．７０６８２～０．７０７７０，εＮｄ（Ｔ）＝－７．４２～－３．２２］。流纹质岩石总体具富碱、富硅、富铝，贫钙、贫镁特征，其Ｒｂ、Ｔｈ等元素的含量较高，而Ｂａ、Ｓｒ、Ｔｉ、Ｐ等元素含量则明显偏低，并具显著的铕负异常（δＥｕ＝０．１６～０．４４），岩石的εＮｄ（Ｔ）值变化于－５．９３～－２．２２。Ⅰ、Ⅱ旋回玄武岩和流纹岩在地球化学特征上均具明显变异。根据对火山岩地球化学特征的综合分析表明，玄武岩主要为幔源岩浆与下部地壳岩石相互作用的产物，而流纹岩则为玄武岩浆与上部地壳物质进行热及成分交换的结果，不同旋回的玄武岩和流纹岩有不同的源区，为多次脉动分层部分熔融的产物。
The
rock associations of the first and second cycle of early Cretaceous Shimaosh an Group at
Yunshan caldera, Yongtai County, are composed of sedimentary rocks_b asic lava_acidic
volcanic rocks. Intermediate volcanic rocks are absent in thes e rock associations; therefore,
they can be classified as typical bimodal volcan ic rock associations, Geochemically, basaltic
volcanic rocks in these bimodal r ock associations are rich in alkali (especially potassium),
aluminum, iron, LILE and LREE and poor in magnesium, HFSE and siderophile elements, and
have relativ ely high I sr ratios and obviously low ε Nd ( T ) values ( I sr
=0.70682～0.70770, ε Nd ( T )=-7.42～ 3.22). Rhyolitic vol canic rocks are generally
characterized by rich alkali, silicon, aluminum, and p oor calcium, magnesium. They have
relatively high Rb, Th and rather low Ba, Sr, Ti, P, and exhibit obviously negative europium
anomaly (δEu=0.16～0.44). The ε Nd ( T ) values of the rhyolitic volcanic rocks
range from -5.9 3 to -2.22. Basalts and rhyolites in different cycles show clear geochemical var
iance. On the basis of an integrated analysis of the geochemical features of th ese volcanic
rock associations, this paper concludes that the basalts originat ed mainly from interaction
between mantle_derived magma and low_crustal materi als, and rhyolitic volcanic rocks
resulted from thermal and chemical interaction between basaltic magma and the upper part of
crustal materials. Basalts and rhy olites in different cycles have different source regions, and
they are products of multiperiodic pulsive layer partial melting.
出处
《岩石矿物学杂志》
CAS
CSCD
北大核心
1999年第2期97-107,共11页
Acta Petrologica et Mineralogica
基金
国家自然科学基金
高等学校博士学科点专项科研基金
关键词
双峰式火山岩
地球化学
岩石成因
福建
火山岩
: bimodal volcanic
rock
geochemistry
petrogenesis
Yun shan caldera, Yongtai County, Fujian Province
